1. Field of the Invention
The present invention relates in general to brake assemblies for actuating the brakes of a trailer being towed and more specifically to such assemblies that include means for controlling brake activation such that the brakes are activated only when certain predetermined conditions exist.
2. Description of the Prior Art
A wide variety of hitch and trailer brake assemblies for actuating the trailer brakes of a trailer are known in the art. A typical form of such assemblies includes two telescoping members, one of which is connected to the trailer and the other of which is connected to the towing or tractor vehicle. On deceleration of the tractor with respect to the trailer the resultant relative movement between the telescoping members provides for the activation of a hydraulic unit to supply hydraulic fluid under pressure to the trailer brakes.
Under most operating conditions, the above-described assemblies provides satisfactory brake actuation. However, these assemblies can create problems under certain conditions of road operation, for example mountain driving wherein the towing vehicle is often geared down for braking purposes. Under such conditions, the weight or coasting action of the trailer actuates the hydraulic unit to the trailer brakes. Heating of the trailer brakes results so as to often times effect a fading of the trailer brakes upon their later use.
One approach in compensating for the above problem is described in a U.S. Patent to Horne, No. 2,407,156, issued Sept. 3, 1946. The assembly disclosed by Horne includes a hydraulic unit mounted on a trailer tongue having a piston member attached to a vehicle. Consequently, when the vehicle is decelerated with respect to the trailer, the piston member is retracted to supply fluid under pressure for application to the trailer brake system. The piston acts against a coil spring having an adjustable pressure to provide a spring force that must be overcome before retractive movement of the piston can take place. Thus, the Horne assembly maintains the brakes of the trailer inoperative until a predetermined minimum force is exerted on the piston due to relative movement between the trailer and its towing vehicle. Fluid is thus supplied to the trailer brakes when the trailer force applied on the piston exceeds the initial spring pressure acting on the piston. The spring thus functions merely to dampen a free piston movement.
The present invention differs from the Horne assembly in that it includes a valve means interposed between a source of fluid under pressure and the trailer brake system to provide a precise means for controlling trailer brake actuation. Moreover, the valve means totally blocks fluid flow to the brake system until a predetermined fluid pressure is reached, at which time fluid is supplied to the brake system at or above the predetermined pressure. Trailer brake operation is thus positively eliminated during down hill travel, or trailer back-up operation, until the predetermined fluid pressure is obtained.